Electrostatic spray gun

Abstract

An electrostatic spray gun is disclosed which comprises a high valued resistance in the barrel portion of the gun, and a second resistor in the nozzle of the gun closely adjacent to a charging electrode projecting from the nozzle to provide safer operation.

Having described my invention I claim: 
     
       1. An electrostatic coating apparatus comprising: a nozzle portion made from substantially nonconductive material, having a fluid discharge opening and effective to project a dispersed cloud of coating material therefrom;   a small electrode extending from said nozzle portion;   a coating material conduit in communication with said fluid discharge opening;   a high voltage electrical path passing through the nozzle portion and adapted to connect said electrode to a source of high voltage electrical power; and   at least a first series resistor in said electrical path located in said nozzle portion said first series resistor being in at least the megohm range.   
     
     
       2. The apparatus of claim 1 which further comprises a second series resistor in said electrical path located such that said first series resistor is located between said second series resistor and said electrode. 
     
     
       3. The apparatus of claim 2 wherein said first resistor has a smaller resistance value than said second resistor. 
     
     
       4. The apparatus of claim 2 wherein said apparatus is adapted to atomize liquid coating material, and which further comprises: a barrel portion adapted to have said nozzle portion attached thereto, wherein said coating material conduit and said electrical path pass through said barrel portion to said nozzle portion and wherein said second resistor is located in said barrel portion.   
     
     
       5. The apparatus of claim 4 wherein said first resistor is smaller than said second resistor. 
     
     
       6. The apparatus of claim 5 wherein the resistance of said first resistor is smaller than the resistance of said second resistor. 
     
     
       7. An electrostatic coating apparatus comprising: a barrel portion having a fluid conduit and a high voltage electrical path therein, one end of said fluid conduit being adapted to be connected to a source of fluid under pressure, and wherein one end of said electrical path is adapted to be connected to a source of high voltage electrical power and wherein a second end of said electrical path in said barrel is adapted to be connected to another electrical path;   a substantially non-conductive nozzle connected to said barrel and having a fluid conduit and high voltage electrical path therein and a thin electrode extending therefrom, said fluid conduit in said nozzle being in communication with said fluid conduit in said barrel and said electrical path in said nozzle having a first end connected to said electrode and a second end connected to said second end of said electrical path in said barrel, said electrical path in said nozzle comprising at least a first series resistor in the megohm range connected to said electrode.   
     
     
       8. The apparatus of claim 7 wherein said high voltage electrical path in said barrel comprises a series resistor having a larger resistance value than said first series resistance in said nozzle. 
     
     
       9. The apparatus of claim 8 wherein said electrode is approximately 0.69 inches in length, said first resistor has a value of approximately 12 megohms, and said second resistor has a value of approximately 75 megohms. 
     
     
       10. The apparatus of claim 9 wherein said electrode is approximately 0.025 inches in diameter. 
     
     
       11. The apparatus of claim 10 wherein one end of said electrode projects approximately 0.27 inches beyond the end of said nozzle. 
     
     
       12. The apparatus of claim 8 wherein said second resistor is axially positioned in a bore in said nozzle and secured therein by means of a spring type electrical connector. 
     
     
       13. The apparatus of claim 12 wherein said bore is the fluid conduit in said nozzle. 
     
     
       14. An electrostatic spray coating apparatus comprising: a barrel portion having: a fluid conduit therein adapted to have one end connected to a source of fluid under pressure; and a first resistor in the megohm range in said barrel and having a first and second end, said first end being adapted to be connected to a source of high voltage electrical power;   a removable air atomizing nozzle attached to said barrel portion and made from substantially non-conductive material, and having: a fluid discharge orifice; a fluid conduit in fluid communication with said orifice and with the fluid conduit in the barrel portion; and a thin electrode extending from said nozzle; and   a second resistor located in said nozzle with one end connected to said electrode and the other end electrically connected to the second end of said first resistor.   
     
     
       15. The apparatus of claim 14 wherein the second resistor is located in the fluid conduit of the nozzle. 
     
     
       16. The apparatus of claim 15 wherein the resistor is sealed into a container chemically resistant and abrasion resistant to coating materials to be sprayed from said gun and with electrical connections for said second resistor at its ends, wherein the fluid in said conduit flows around the container. 
     
     
       17. A method of electrostatic spray coating comprising the steps of: dispensing a disperse coating material toward an object to be coated from a substantially electrically nonconductive nozzle;   imparting an electrical charge to said coating material by means of a small electrode extending from the nozzle;   supplying high voltage electrical power from an electrical power source to said electrode, sufficient to impart said charge to said coating material;   dissipating electrical energy supplied to said electrode through at least a first resistor in the megohm range located in said nozzle.   
     
     
       18. The method of claim 17 which further comprises the step of dissipating electrical energy supplied to said electrode through a second resistor located between said first resistor and said power source. 
     
     
       19. The method of claim 18 which further comprises the step of: supplying said electrical power to said electrode through a barrel supporting said nozzle and locating said second resistor in said barrel.   
     
     
       20. The method of claim 19 wherein said first resistor has a resistance value of at least several megohms and said second resistor has a higher resistance value than said first resistor. 
     
     
       21. A method of electrostatic spray coating comprising the steps of: dispensing a disperse cloud of coating material toward an object to be coated from a substantially electrically non-conductive nozzle;   imparting an electrical charge to said coating material by means of a small electrode extending from the nozzle;   supplying high voltage electrical power to said electrode from an electrical power source sufficient to impart said charge on said coating material, through at least a first resistor in at least the megohm range located in said nozzle.   
     
     
       22. The method of claim 21 which further comprises the step of: supporting said nozzle by means of a substantially electrically non-conductive barrel; and   wherein the step of supplying said high voltage electrical power to said electrode further comprises the step of supplying said electrical power to said electrode through a second resistor located in said barrel, and having a larger resistance than said first resistor.